What is the use of class declaration in c++

Question

I was going through a c++ code and saw a header file with below declaration:

file a.h
class xyz;

But that class was not defined any where in the file. I also wrote a code and it perfectly compiles fine. Just wanted to know what is the use of declaring a class like this as it does't enforces programmer to define.

Thanks in advance!!

Thanks Ninja for pointing out. I didn't knew the term Forward declaration. — neo, May 14 '14 at 19:15

score 0 · Answer 1 · answered May 14 '14 at 19:12

0

this is a forward declaration of a class. you can use xyz* variables in the header file - the linker will resolve the actual class implementation later

answered May 14 '14 at 19:12

NirMH

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score 0 · Answer 2 · answered May 14 '14 at 19:12

That's a forward declaration (or simply declaration) and it allows you to use the name xyz in contexts where a full definition isn't required.

One example is when you have another class which contains a pointer to a xyz:

class xyz;
class Aux
{
  xyz* k;
};

Other uses are return types, parameter types and references.

What is the use of class declaration in c++

2 Answers2